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Merge pull request #552 from cpunion/async-functions

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Async functions design
This commit is contained in:
xushiwei
2024-07-24 12:04:18 +08:00
committed by GitHub
parent 74cc12133e 89bdb315d5
commit 1eb9775f34
3 changed files with 536 additions and 48 deletions
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171
x/io/README.md
View File

@@ -36,9 +36,8 @@ async function asyncCall(): Promise<string> {
return `AsyncCall: ${result}`;
}
async function asyncCall2(): Promise<string> {
const result = await resolveAfter1Second();
return `AsyncCall2: ${result}`;
function asyncCall2(): Promise<string> {
return resolveAfter1Second();
}
function asyncCall3(): void {
@@ -92,9 +91,8 @@ async def async_call() -> str:
result = await resolve_after_1_second()
return f"AsyncCall: {result}"
async def async_call2() -> str:
result = await resolve_after_1_second()
return f"AsyncCall2: {result}"
def async_call2() -> asyncio.Task:
return resolve_after_1_second()
def async_call3() -> None:
asyncio.create_task(print_after_1_second())
@@ -139,7 +137,9 @@ async fn name(param0: Type) -> ReturnType {
Example:
```rust
use tokio::time::{sleep, Duration};
use std::time::Duration;
use tokio::time::sleep;
use std::future::Future;
async fn resolve_after_1_second() -> String {
sleep(Duration::from_secs(1)).await;
@@ -151,9 +151,8 @@ async fn async_call() -> String {
format!("AsyncCall: {}", result)
}
async fn async_call2() -> String {
let result = resolve_after_1_second().await;
format!("AsyncCall2: {}", result)
fn async_call2() -> impl Future<Output = String> {
resolve_after_1_second()
}
fn async_call3() {
@@ -177,7 +176,7 @@ async fn main() {
async_call3();
// Wait for AsyncCall3 to complete
sleep(Duration::from_secs(1)).await;
sleep(Duration::from_secs(2)).await;
println!("Main function completed");
}
@@ -216,10 +215,9 @@ class Program
return $"AsyncCall: {result}";
}
static async Task<string> AsyncCall2()
static Task<string> AsyncCall2()
{
string result = await ResolveAfter1Second();
return $"AsyncCall2: {result}";
return ResolveAfter1Second();
}
static void AsyncCall3()
@@ -286,8 +284,7 @@ cppcoro::task<std::string> asyncCall() {
}
cppcoro::task<std::string> asyncCall2() {
auto result = co_await resolveAfter1Second();
co_return "AsyncCall2: " + result;
return resolveAfter1Second();
}
cppcoro::task<void> asyncCall3() {
@@ -323,3 +320,145 @@ int main() {
return 0;
}
```
## Common concepts
### Promise, Future, Task, and Coroutine
- **Promise**: An object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. It is used to produce a value that will be consumed by a `Future`.
- **Future**: An object that represents the result of an asynchronous operation. It is used to obtain the value produced by a `Promise`.
- **Task**: A unit of work that can be scheduled and executed asynchronously. It is a higher-level abstraction that combines a `Promise` and a `Future`.
- **Coroutine**: A special type of function that can suspend its execution and return control to the caller without losing its state. It can be resumed later, allowing for asynchronous programming.
### `async`, `await` and similar keywords
- **`async`**: A keyword used to define a function that returns a `Promise` or `Task`. It allows the function to pause its execution and resume later.
- **`await`**: A keyword used to pause the execution of an `async` function until a `Promise` or `Task` is resolved. It unwraps the value of the `Promise` or `Task` and allows the function to continue.
- **`co_return`**: A keyword used in C++ coroutines to return a value from a coroutine. It is similar to `return` but is used in coroutines to indicate that the coroutine has completed. It's similar to `return` in `async` functions in other languages that boxes the value into a `Promise` or `Task`.
`async/await` and similar constructs provide a more readable and synchronous-like way of writing asynchronous code, it hides the type of `Promise`/`Future`/`Task` from the user and allows them to focus on the logic of the code.
### Executing Multiple Async Operations Concurrently
To run multiple promises concurrently, JavaScript provides `Promise.all`, `Promise.allSettled` and `Promise.any`, Python provides `asyncio.gather`, Rust provides `tokio::try_join`, C# provides `Task.WhenAll`, and C++ provides `cppcoro::when_all`.
In some situations, you may want to get the first result of multiple async operations. JavaScript provides `Promise.race` to get the first result of multiple promises. Python provides `asyncio.wait` to get the first result of multiple coroutines. Rust provides `tokio::select!` to get the first result of multiple futures. C# provides `Task.WhenAny` to get the first result of multiple tasks. C++ provides `cppcoro::when_any` to get the first result of multiple tasks. Those functions are very simular to `select` in Go.
### Error Handling
`await` commonly unwraps the value of a `Promise` or `Task`, but it also propagates errors. If the `Promise` or `Task` is rejected or throws an error, the error will be thrown in the `async` function by the `await` keyword. You can use `try/catch` blocks to handle errors in `async` functions.
## Common patterns
- `async` keyword hides the types of `Promise`/`Future`/`Task` in the function signature in Python and Rust, but not in JavaScript, C#, and C++.
- `await` keyword unwraps the value of a `Promise`/`Future`/`Task`.
- `return` keyword boxes the value into a `Promise`/`Future`/`Task` if it's not already.
## Design considerations in LLGo
- Don't introduce `async`/`await` keywords to compatible with Go compiler (just compiling)
- For performance reason don't implement async functions with goroutines
- Avoid implementing `Promise` by using `chan` to avoid blocking the thread, but it can be wrapped as a `chan` to make it compatible `select` statement
## Design
Introduce `Promise` type to represent an asynchronous operation and its resulting value. `Promise` can be resolved with a value with an error. `Promise` can be awaited to get the value and error.
`Promise` just a type indicating the asynchronous operation, it can't be created and assigned directly. It be replaced to `PromiseImpl` by the LLGo compiler.
```go
// Some native async functions
func timeoutAsync(d time.Duration, cb func()) {
go func() {
time.Sleep(d)
cb()
}()
}
// Wrap callback-based async function into Promise
func resolveAfter1Second() (resolve Promise[string]) {
timeoutAsync(1 * time.Second, func() {
resolve("Resolved after 1 second", nil)
})
}
// Compiled to:
func resolveAfter1Second() (resolve PromiseImpl[string]) {
promise := io.NewPromiseImpl[string](resolve func(value string, err error) {
resolve: func(value string, err error) {
for true {
switch (promise.prev = promise.next) {
case 0:
timeoutAsync(1 * time.Second, func() {
resolve("Resolved after 1 second", nil)
})
}
}
},
}
return promise
}
func asyncCall() (resolve Promise[string]) {
str, err := resolveAfter1Second().Await()
resolve("AsyncCall: " + str, err)
}
// Compiled to:
func asyncCall() (resolve PromiseImpl[string]) {
promise := io.NewPromiseImpl[string](resolve func(value string, err error) {
for true {
switch (promise.prev = promise.next) {
case 0:
resolveAfter1Second()
return
case 1:
str, err := promise.value, promise.err
resolve("AsyncCall: " + str, err)
return
}
}
})
return promise
}
// Directly return Promise
func asyncCall2() Promise[string] {
return resolveAfter1Second()
}
// Compiled to:
func asyncCall2() PromiseImpl[string] {
return resolveAfter1Second()
}
// Don't wait for Promise to complete
func asyncCall3() {
resolveAfter1Second().Then(func(result string) {
fmt.Println("AsyncCall3: " + result)
})
}
func asyncMain() {
fmt.Println("Starting AsyncCall")
result1 := asyncCall().Await()
fmt.Println(result1)
fmt.Println("Starting AsyncCall2")
result2 := asyncCall2().Await()
fmt.Println(result2)
fmt.Println("Starting AsyncCall3")
asyncCall3()
// Wait for AsyncCall3 to complete
time.Sleep(2 * time.Second)
fmt.Println("Main function completed")
}
```

298
x/io/_demo/asyncdemo/async.go
View File

@@ -1,40 +1,290 @@
package main
import (
"encoding/json"
"fmt"
"log"
"time"
"github.com/goplus/llgo/x/io"
)
var GetUser = io.Async[any](func(string) any {
panic("todo: GetUser")
})
// -----------------------------------------------------------------------------
var GetScore = io.Async[float64](func() float64 {
type Response struct {
StatusCode int
mockBody string
}
func (r *Response) mock(body string) {
r.mockBody = body
}
func (r *Response) Text() (resolve io.Promise[string]) {
resolve(r.mockBody, nil)
return
}
func (r *Response) TextCompiled() *io.PromiseImpl[string] {
P := &io.PromiseImpl[string]{}
P.Func = func(resolve func(string, error)) {
for {
switch P.Prev = P.Next; P.Prev {
case 0:
resolve(r.mockBody, nil)
P.Next = -1
return
default:
panic("Promise already done")
}
}
}
return P
}
func HttpGet(url string, callback func(resp *Response, err error)) {
resp := &Response{StatusCode: 200}
callback(resp, nil)
}
func AsyncHttpGet(url string) (resolve io.Promise[*Response]) {
HttpGet(url, resolve)
return
}
func AsyncHttpGetCompiled(url string) *io.PromiseImpl[*Response] {
P := &io.PromiseImpl[*Response]{}
P.Func = func(resolve func(*Response, error)) {
for {
switch P.Prev = P.Next; P.Prev {
case 0:
HttpGet(url, resolve)
P.Next = -1
return
default:
panic("Promise already done")
}
}
}
return P
}
// -----------------------------------------------------------------------------
type User struct {
Name string
}
func GetUser(uid string) (resolve io.Promise[User]) {
resp, err := AsyncHttpGet("http://example.com/user/" + uid).Await()
if err != nil {
resolve(User{}, err)
return
}
if resp.StatusCode != 200 {
resolve(User{}, fmt.Errorf("http status code: %d", resp.StatusCode))
return
}
resp.mock(`{"name":"Alice"}`)
body, err := resp.Text().Await()
if err != nil {
resolve(User{}, err)
return
}
user := User{}
if err := json.Unmarshal([]byte(body), &user); err != nil {
resolve(User{}, err)
return
}
resolve(user, nil)
return
}
func GetUserCompiled(uid string) *io.PromiseImpl[User] {
var state1 *io.PromiseImpl[*Response]
var state2 *io.PromiseImpl[string]
P := &io.PromiseImpl[User]{}
P.Func = func(resolve func(User, error)) {
for {
switch P.Prev = P.Next; P.Prev {
case 0:
state1 = AsyncHttpGetCompiled("http://example.com/user/" + uid)
P.Next = 1
return
case 1:
state1.EnsureDone()
resp, err := state1.Value, state1.Err
if err != nil {
resolve(User{}, err)
return
}
if resp.StatusCode != 200 {
resolve(User{}, fmt.Errorf("http status code: %d", resp.StatusCode))
return
}
resp.mock(`{"name":"Alice"}`)
state2 = resp.TextCompiled()
P.Next = 2
return
case 2:
state2.EnsureDone()
body, err := state2.Value, state2.Err
if err != nil {
resolve(User{}, err)
return
}
user := User{}
if err := json.Unmarshal([]byte(body), &user); err != nil {
resolve(User{}, err)
return
}
resolve(user, nil)
P.Next = -1
return
default:
panic("Promise already done")
}
}
}
return P
}
func GetScore() *io.Promise[float64] {
panic("todo: GetScore")
})
}
var DoUpdate = io.Async[io.Void](func(op string) io.Void {
func GetScoreCompiled() *io.PromiseImpl[float64] {
P := &io.PromiseImpl[float64]{}
P.Func = func(resolve func(float64, error)) {
for {
switch P.Prev = P.Next; P.Prev {
case 0:
panic("todo: GetScore")
default:
panic("Promise already done")
}
}
}
return P
}
func DoUpdate(op string) *io.Promise[io.Void] {
panic("todo: DoUpdate")
})
}
func DoUpdateCompiled(op string) *io.PromiseImpl[io.Void] {
P := &io.PromiseImpl[io.Void]{}
P.Func = func(resolve func(io.Void, error)) {
for {
switch P.Prev = P.Next; P.Prev {
case 0:
panic("todo: DoUpdate")
default:
panic("Promise already done")
}
}
}
return P
}
func Demo() (resolve io.Promise[io.Void]) {
user, err := GetUser("123").Await()
log.Println(user, err)
user, err = io.Race[User](GetUser("123"), GetUser("456"), GetUser("789")).Await()
log.Println(user, err)
users, err := io.All[User]([]io.AsyncCall[User]{GetUser("123"), GetUser("456"), GetUser("789")}).Await()
log.Println(users, err)
user, score, _, err := io.Await3[User, float64, io.Void](GetUser("123"), GetScore(), DoUpdate("update sth."))
log.Println(user, score, err)
// TODO(lijie): select from multiple promises without channel
select {
case user := <-GetUser("123").Chan():
log.Println("user:", user)
case score := <-GetScore().Chan():
log.Println("score:", score)
case <-io.Timeout(5 * time.Second).Chan():
log.Println("timeout")
}
return
}
func DemoCompiled() *io.PromiseImpl[io.Void] {
var state1 *io.PromiseImpl[User]
var state2 *io.PromiseImpl[User]
var state3 *io.PromiseImpl[[]User]
var state4 *io.PromiseImpl[io.Await3Result[User, float64, io.Void]]
P := &io.PromiseImpl[io.Void]{}
P.Func = func(resolve func(io.Void, error)) {
for {
switch P.Prev = P.Next; P.Prev {
case 0:
state1 = GetUserCompiled("123")
P.Next = 1
return
case 1:
state1.EnsureDone()
user, err := state1.Value, state1.Err
log.Printf("user: %v, err: %v\n", user, err)
state2 = io.Race[User](GetUserCompiled("123"), GetUserCompiled("456"), GetUserCompiled("789"))
P.Next = 2
return
case 2:
state2.EnsureDone()
user, err := state2.Value, state2.Err
log.Println(user, err)
state3 = io.All[User]([]io.AsyncCall[User]{GetUserCompiled("123"), GetUserCompiled("456"), GetUserCompiled("789")})
P.Next = 3
return
case 3:
state3.EnsureDone()
users, err := state3.Value, state3.Err
log.Println(users, err)
state4 = io.Await3Compiled[User, float64, io.Void](GetUserCompiled("123"), GetScoreCompiled(), DoUpdateCompiled("update sth."))
P.Next = 4
return
case 4:
state4.EnsureDone()
user, score, _, err := state4.Value.V1, state4.Value.V2, state4.Value.V3, state4.Value.Err
log.Println(user, score, err)
select {
case user := <-GetUserCompiled("123").Chan():
log.Println("user:", user)
case score := <-GetScoreCompiled().Chan():
log.Println("score:", score)
case <-io.TimeoutCompiled(5 * time.Second).Chan():
log.Println("timeout")
}
P.Next = -1
return
default:
panic("Promise already done")
}
}
}
return P
}
func main() {
user, err := GetUser("123").Await()
fmt.Println(user, err)
user, err = io.Race(GetUser("123"), GetUser("456"), GetUser("789")).Await()
fmt.Println(user, err)
user, score, _, err := io.Await3[any, float64, io.Void](GetUser("123"), GetScore(), DoUpdate("update sth."))
fmt.Println(user, score, err)
select {
case user := <-GetUser("123"):
fmt.Println("user:", user)
case score := <-GetScore():
fmt.Println("score:", score)
case <-io.Timeout(5 * time.Second):
fmt.Println("timeout")
}
log.SetFlags(log.Lshortfile | log.LstdFlags)
// io.Run(Demo())
io.Run(DemoCompiled())
}

115
x/io/io.go
View File

@@ -30,21 +30,40 @@ type Void = [0]byte
// -----------------------------------------------------------------------------
type AsyncCall[OutT any] chan OutT
type AsyncCall[OutT any] interface {
Await(timeout ...time.Duration) (ret OutT, err error)
Chan() <-chan OutT
EnsureDone()
}
// llgo:link AsyncCall.Await llgo.await
func (AsyncCall[OutT]) Await(timeout ...time.Duration) (ret OutT, err error) {
func Await[OutT any](call AsyncCall[OutT], timeout ...time.Duration) (ret OutT, err error) {
return
}
//go:linkname Timeout llgo.timeout
func Timeout(time.Duration) (ret AsyncCall[Void])
func TimeoutCompiled(d time.Duration) *PromiseImpl[Void] {
P := &PromiseImpl[Void]{}
P.Func = func(resolve func(Void, error)) {
go func() {
time.Sleep(d)
resolve(Void{}, nil)
}()
}
return P
}
// llgo:link Race llgo.race
func Race[OutT any](acs ...AsyncCall[OutT]) (ret AsyncCall[OutT]) {
func Race[OutT any](acs ...AsyncCall[OutT]) (ret *PromiseImpl[OutT]) {
return
}
func All[OutT any](acs []AsyncCall[OutT]) (ret *PromiseImpl[[]OutT]) {
return nil
}
// llgo:link Await2 llgo.await
func Await2[OutT1, OutT2 any](
ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2],
@@ -52,6 +71,18 @@ func Await2[OutT1, OutT2 any](
return
}
type Await2Result[T1 any, T2 any] struct {
V1 T1
V2 T2
Err error
}
func Await2Compiled[OutT1, OutT2 any](
ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2],
timeout ...time.Duration) (ret *PromiseImpl[Await2Result[OutT1, OutT2]]) {
return
}
// llgo:link Await3 llgo.await
func Await3[OutT1, OutT2, OutT3 any](
ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2], ac3 AsyncCall[OutT3],
@@ -59,13 +90,81 @@ func Await3[OutT1, OutT2, OutT3 any](
return
}
// -----------------------------------------------------------------------------
type Await3Result[T1 any, T2 any, T3 any] struct {
V1 T1
V2 T2
V3 T3
Err error
}
type Promise[OutT any] func(...any) AsyncCall[OutT]
// llgo:link Async llgo.async
func Async[OutT any](fn any) (ret Promise[OutT]) {
func Await3Compiled[OutT1, OutT2, OutT3 any](
ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2], ac3 AsyncCall[OutT3],
timeout ...time.Duration) (ret *PromiseImpl[Await3Result[OutT1, OutT2, OutT3]]) {
return
}
func Run(ac AsyncCall[Void]) {
p := ac.(*PromiseImpl[Void])
p.Resume()
<-ac.Chan()
}
// -----------------------------------------------------------------------------
type Promise[OutT any] func(OutT, error)
// llgo:link Promise.Await llgo.await
func (p Promise[OutT]) Await(timeout ...time.Duration) (ret OutT, err error) {
return
}
func (p Promise[OutT]) Chan() <-chan OutT {
return nil
}
func (p Promise[OutT]) EnsureDone() {
}
// -----------------------------------------------------------------------------
type PromiseImpl[TOut any] struct {
Func func(resolve func(TOut, error))
Value TOut
Err error
Prev int
Next int
c chan TOut
}
func (p *PromiseImpl[TOut]) Resume() {
p.Func(func(v TOut, err error) {
p.Value = v
p.Err = err
})
}
func (p *PromiseImpl[TOut]) EnsureDone() {
if p.Next == -1 {
panic("Promise already done")
}
}
func (p *PromiseImpl[TOut]) Chan() <-chan TOut {
if p.c == nil {
p.c = make(chan TOut, 1)
p.Func(func(v TOut, err error) {
p.Value = v
p.Err = err
p.c <- v
})
}
return p.c
}
func (p *PromiseImpl[TOut]) Await(timeout ...time.Duration) (ret TOut, err error) {
panic("should not called")
}
// -----------------------------------------------------------------------------